The miniaturization of semiconductor components is accorded a preeminent importance in the development of new generations of semiconductor technologies. By shrinking the dimensions of the semiconductor components, it is possible to increase the integration density on a semiconductor chip and thus to achieve a cost saving as an important development goal. However, shrinking the component dimensions requires dopant profiles which can be produced ever more steeply and in ever more sharply delimited fashion. Particularly for contact regions which, on the one hand, are intended to have extremely high dopant concentrations in order to obtain a low-value contact resistance, but on the other hand must not influence the functionality of the more lightly doped wells situated directly in their vicinity, it is desirable to produce dopant profiles which fall steeply.
One method for producing such dopant profiles is laser annealing in the melt mode. In this case, by way of example, the energy density of an individual light pulse is chosen to be high enough, for instance by focusing that the wafer is melted near the surface. On account of this, previously implanted dopants are dissolved in the melt and incorporated at lattice sites during the recrystallization. A degree of activation of the dopants of up to 100% is obtained in this case. Since the pulse duration is very short, lasting e.g., a few nanoseconds, and only an individual pulse is required for melting the wafer near the surface, an outdiffusion of the dopants is negligibly small in comparison with other methods. Aside from the lower degree of outdiffusion, shorter process durations are obtained with laser annealing in the melt mode in comparison with other methods. Thus, by way of example, an individual pulse during laser annealing in the melt mode may be sufficient for activating the dopants.
During laser annealing in the melt mode, a semiconductor body below a semiconductor body/oxide layer interface that is possibly present is also melted, whereas the oxide does not melt. The subsequent recrystallization leads to thermomechanical strains in the region of the interface. This has undesirable consequences, such as cracking and delamination of the oxide. Consequently, during laser annealing in the melt mode, care must be taken to ensure that oxide-covered regions of the semiconductor body are not exposed to the laser light during annealing. Accordingly, masking is necessary during the annealing.
U.S. Pat. No. 6,291,302 describes a method for producing a field effect transistor that includes depositing a material that reflects laser light onto a substrate having an active region and a non-active region. In this case, regions of the deposited layer above the active region are removed and dopants within the active region are activated by laser annealing. The masking for the laser annealing is removed again after the annealing.
A simplified method for producing semiconductor zones with a steep doping profile would be desirable.
For these and other reasons, there is a need for the present invention.